The present disclosure relates to image capture devices which convert incident light into an electrical signal, and output the electrical signal as a video signal.
Japanese Unexamined Patent Publication No. 2009-174854 describes a distance measuring camera having a function of measuring a distance to an object using infrared light. In general, a solid-state image capture device used in a distance measuring camera is called a distance measuring sensor. In particular, a camera for detecting a motion of the body or hand of a human as a subject, that is, for example, included in a game console, is also called a motion camera.
Japanese Unexamined Patent Publication No. 2000-236486 describes a solid-state image capture device having a vertical transfer electrode structure which allows for simultaneous reading of all pixels. Specifically, the device is a charge coupled device (CCD) image sensor in which a vertical transfer unit extending in the vertical direction is provided adjacent to each column of photodiodes (PDs). The vertical transfer unit includes four vertical transfer electrodes for each photodiode. At least one of the four vertical transfer electrodes also serves as a read electrode which is used to read out signal charge from the photodiode into the vertical transfer unit. The CCD image sensor also includes a vertical overflow drain (VOD) for draining signal charge from the photodiodes of all pixels.
Japanese Unexamined Patent Publication No. 2000-236486 above assumes a situation where the solid-state image capture device is used as a distance measuring sensor. Initially, an image is captured by illumination with infrared light. At this time, signal charge obtained by illumination with infrared light is read from photodiodes located in odd-numbered rows into the vertical transfer unit. Signal charge accumulated in photodiodes located in even-numbered rows is drain off to the substrate. Next, an image is captured without illumination with infrared light. At this time, while the positions of the signal charge in the vertical transfer unit are maintained, signal charge obtained without illumination with infrared light is read from photodiodes located in even-numbered rows into the vertical transfer unit. Signal charge accumulated in photodiodes located in odd-numbered rows is drained off to the substrate. Thereafter, signal charge accumulated in the vertical transfer unit is sequentially transferred and output. By subtracting signal charge obtained without illumination with infrared light from signal charge obtained by illumination with infrared light, a distance image can be obtained from which an influence of an infrared light component in the ambient light has been removed.
However, in this case, the following problems arise. Firstly, when signal charge obtained without illumination with infrared light is subtracted from signal charge obtained by illumination with infrared light, there is a one-pixel difference in position between the former and latter signal charge. This subtraction reduces the resolution in the subtraction direction by a half. Also, the rate of use of signal charge is 50% due to the drainage, resulting in a reduction in sensitivity. In addition, there is a difference in exposure timing between signal charge obtained by illumination with infrared light and signal charge obtained without illumination with infrared light, and therefore, error is likely to occur in the result of distance measurement, particularly when an image of a fast-moving object is captured.